Question 1

What is a gain map image?

Accepted Answer

A gain map image encodes an SDR photo plus a secondary brightness map. On HDR displays (Apple XDR, Android Ultra HDR, Windows Advanced Color) highlights render above SDR reference white. On SDR displays the image renders normally — the format is fully backward compatible.

Question 2

Does Gainmaps upload my photos?

Accepted Answer

No. All processing runs locally in a browser service worker. No file leaves your device. No upload, no server.

Question 3

How do I batch-encode gain map images from the terminal?

Accepted Answer

Install the gainmap CLI: npm install -g gainmap, or brew install kirkstrobeck/tap/gainmap, or curl -fsSL https://gainmaps.com/install.sh | sh.